Internal-combustion engine with rotary piston

ABSTRACT

An engine construction in which a casing has circular and oval sections accommodating a rotatable piston guide ring through which pistons radially reciprocate.

References Cited UN1TED STATES PATENTS 12/1922 McCarthy 6/1940 2,326,913 8/1943 A11stadt.... 4/1946 Harries......................... 8/1965 Kraic et a1. 3,451,381 6/1969 Armstrong et a1............

FOREIGN PATENTS 11/1925 Switzerland Primary- ExaminerE. Wendell Burns F02b 53/00, F02b 55/00 [50] Field of 123/44 R.

Josef Hotmann Krombach. Germany Appl. \'ov 2,991 Filed Jan. 15. I970 [45] Patented Aug.3, 1971 A110 Tankanlagenbau Gmbl-I Nordring, Offenbach am Slain, Germany INTERNAL-COMBUSTION ENGINE WITH ROTARY PISTON 3 Claims, 5 Drawing Figs.

123/8.01,123/8.23, 12318.39, 123/8.45, 123/43 R, 123/44 R, 123/45 R 44 D, 44 C, 44 E, 44 A, 45 R. 45 A, 43 R, 43 L, 8.39, 8.45, 8.27. 8.23, 8.21, 8.19, 8.01

United States Patent [72] Inventor [73] Assignee ifi 4. t

INTERNAL-COMBUSTION ENGINE WITH ROTARY PISTON SUMMARY OF THE INVENTION Field of Invention This invention relates to a rotary piston internal-combustion engine.

The invention provides an engine of the above-noted type in which a cylindrical piston guide ring is pivoted and driven eccentrically inside the crankcase around its axle or shaft and fitting against a concentric part of the casing, there being formed with this casing an expansion chamber which terminates in a gas exhaust passage and contains at most two piston offset at more than 90 to each other, each in its own cylinder being slidably articulated to an axis of rotation mounted eccentrically to the piston guide ring in the casing, and provided with means which, when the guide ring and the reciprocating pistons inside it rotate, keep those pistons constantly in hermetic contact with the casing shell of the expansion chamber. This enables fuel and air for combustion to be supplied to the cylinders in an area of the peripheral casing shell preceding the expansion chamber and to an ignition point in the direction of rotation'of the guide ring, and leaves a compression space open between each piston and the casing shell for the admission of said fuel and air after each piston has made its compression stroke.

BACKGROUND This arrangement of a piston guide ring rotatable around its axle shaft mounted in the casing distinguishes the engine of this invention through the simplicity of its design as against the so-called rocker engine (Wankelmotor) with one rotatingv shaft lying beyond the axle shaft of the crankcase, thus forming an expansion space of almost l80 arc length, up to the forerunning piston, around the likewise cylindrical piston guide ring, the fuel-air mixture inlet running through a central cavity of the piston guide ring and being controlled by slide valves along the cylinder jackets and through the cylinders back to the compression chambers. The cylinders of the twopistons are designed in each one of these slide valves, which are radially slide mounted inside the piston guide ring and are steadily forced against the cylindrical inner wall of the casing.

along a surface line thereof while the piston guide ring rotates.

At the radially external end of the sleeve valve, compression.

chambers are constructed each with its assigned spark plug which rotates together with the piston guide ring and the sleeve valves. The pistons are each articulated by an individual connecting rod to a common piston shaft which is supported eccentrically inside the piston guide ring with regard to the latters axis of rotation and also eccentrically to the crankcase axle shaft, in such a way that when the piston guide ring goes through a rotation of 360 each of the pistons makes one suction stroke and one compression stroke. Ignition follows this at a point in the rotation of the piston guide ring, where the latter rests for only a narrow sector on the casing shell, the point itself being situated in the direction of rotation close behind the combustion gas exhaust passage.

The aforesaid known rotational piston internal-combustion engine has the disadvantage that the narrow sector of the easing between the expansion chamber and the combustion gas exhaust passage within which the piston guide ring rests on the casing wall can be sealed off only with difficulty against waste gas reflux directly into the exhaust passage.

Furthermore, the gases expanded between this piston and the succeeding piston can expand no further and are even again compressed to some extent until the leading piston has passed as far as the gas exhaust passage. This means a loss of energy on the expulsion of the burned gases and possibly even some righting moment onto the piston coming up behind which at that point is working on expansion.

Considerable disadvantages reside also in the complex overall design of the known rotational piston engine, because beside a slidable pair of pistons it requires in addition a precision fitted and at the same time radially movable sleeve valve for each piston, and because further only with the greatest difficult can the ignition voltage for two ignition points or two spark plugs, which are mounted to rotate on the piston guide ring, be conveyed to that rotating part. Further difficulties v arise from the central fuel-air mixture supply, which demands that all of the lateral faces of the piston guide ring toward the casing wall must be satisfactorily sealed against radial invasion of gases, which as is clearly known involves peculiar difficulties on account of the high speed of the piston guide ring.

In another form of rotational piston internal-combustion engine of the last-mentioned type (French Pat. 806,689), two concentrically rotatable guide rings are provided for the sleeve valves and pistons, the outer ring running concentrically to the inside shell of the crankcase and fitting against it, and the inner ring forming an annular space with the outer one, into which space one of the combustion chambers of the two sleeve valves pushes its way alternately with the other at a given time. The annular space between the two piston valve guides of the inner piston guide ring is secured on one of its halves by a fixed ring segment, which fits in with concentric surfaces on the inside of the outer piston guide ring and on the outside of the inner piston guide ring. For this reason, the whole design and assembly of the engine is still more complicated than in the last-mentioned embodiment and results in increased losses by frictional wear of the two rotating piston rings on the annular segment without there being any mechanical or thermodynamic advantages of any kind and without any of the drawbacks of the design previously mentioned being appreciably eliminated. The concentric circular form of the working space over an arc of slightly more than 180 may, admittedly, offer more favorable compression ratios, but this does not outweigh the disadvantages of the fixed segment and multitude of frictional surfaces and the further disadvantages inherent in rotating ignition units.

The disadvantages of' the known rotational piston engines, especially insofar as they arise from the unfavorable seating of the piston guide ring relative to the casing wall are partly avoided in a known rotational piston engine (French Pat. 1,315,555) which is of thedesignmentioned at the outset, and in which moreover the inside casing wall running peripherally concentric to the piston guide ring rests hermetically tight thereon in the area of the peripheral casing wall between the gas exhaust passage and the point of ignition, that is within the region of the suction stroke and compression stroke of each piston. Nevertheless adequate utilization of the combustion gases and a practically serviceable engine efficiency is not obtainable, because the expansion space extends only over a small arc of about 20 and has, accordingly, a very slight radial height and correspondingly small volume. This construction is fundamentally restricted by the'fact that four pistons and cylinders, offset at intervals of between them, are provided in the guide ring. The expansion space cannot, therefore, even with a different seating of the common crankshaft, be increased on any account to even approximately 90 of arc, since the expansion of combustion gases in the expansion space would as a rule act not only as a positive thrust on the leading piston in that expansion space but also as a righting moment on the piston coming up 90 behind it. As soon as this latter enters the expansion space, the leading piston forcefully lunges toward the gas exhaust passage. To avoid such a efficiency-decreasing righting moment, and its concomitant engine knock, a further certain length of arc of the guide ring has to rest tightly on the peripheral casing wall between the expansion space and the pistonadvancing on it at any given time in order to avoid any gas reflux onto the leading face of the upcoming piston. Therefore, the expansion space can never attain a 90 length of arc but only an arc length inferior to 90 with a correspondingly small radial height.

Such a small expansion space is, however, most undesirable from the viewpoint of satisfactory utilization of burned gases as already stated, and the invention endeavors to produce rather an expansion space approximately more nearly 180 with a corresponding considerably radial depth. The invention therefore starts off from a rotational piston internal-combustion engine of the design mentioned at the beginning hereof, in which, diverging from the last-mentioned design, the number of pistons and cylinders is restricted to two at the most.

The object of the invention is to eliminate the disadvantages of the said know designs mentioned above and to provide in particular an increased utilization of combustion gases with correspondingly enhanced efficiency.

These purposes of the invention are attained by the inside casing wall, which runs in specifically known manner concentric to the piston guide ring, resting tightly on said piston guide ring in the area of the peripheral casing where the suction stroke and compression stroke of each of the pistons occur, namely between the gas exhaust passage and nearly up to the ignition point, and by the section of the inside wall running eccentrically to the axle shaft of the guide ring at the periphery and opposite this area forming with same an expansion space of uniform aspect and with an arc length greater than 90.

-As only two pistons are provided, offset of course 180 by preference, in the guide ring, the arc length of the expansion space can be substantially greater than 90 and this can be extended, counting up to the center of the gas exhaust passage, preferably through about 180 length of arc.

The articulation of the pistons and the arrangement of the two stator bores are preferably such that each of the pistons on entry into the expansion chamber, that is on leaving the inner portion of the casing wall periphery which is concentric with the piston guide ring, will have finished its compression stroke in the piston guide ring and the previously indrawn medium is exclusively and highly compressed in the residual compression chamber, formed between the piston and the casing wall. The piston then begins on entry into the expansion chamber to protrude from the piston guide ring in such a way that it fits over the whole wall of the expansion chamber up to its end, namely as far as its exhaust passage, sitting tightly all around on the aforesaid wall. Shortly after its entry into the expansion chamber the piston passes over the ignition point or spark plug where instant ignition of the fuel-air mixture takes place. The expansion of the ignited fuel-air mixture drives the piston through the expansion chamber while at the same time its front end in the direction of rotation thrusts the gases burned in the preceding ignition process and expansion process toward the exhaust port located at the end of the expansion chamber. Beyond this outlet orifice the piston proceeds to the area into which the piston guide ring with its peripheral wall fits concentrically and tightly on the concentric portion of the peripheral wall of the crankcase. The piston starts its suction stroke in this area, that is, with the movement into the interior of its cylinder. The inlet for the medium to be drawn in is provided at a suitable point of this area, that is in the case of a carburetor engine for a fuel-air mixture coming from the carburetor. If needed, fuel can be fed by a priming pump additionally through a supply pipe leading to this casing inlet.

Immediately after this filling process the piston compression stroke starts, which ends with its entry into the expansion chamber. The piston guide ring can be connected through a gear drive or directly to the driving shaft and transfers to this the torque exerted in the expansion chamber on the piston projecting here over the piston guide ring and from this onto the piston guide ring. The working cycle described is repeated with the next succeeding piston in the direction of rotation. As i evident, one or two pistons operating in this way can be supported in one and the same piston guide ring each in one cylinder. Mechanically the simplest operating relations result with an arrangement of two pistons whose cylinders are facing one another diametrically in the piston guide ring.

As can be seen, simpler construction, simpler assembly and simpler manufacture of the engine is obtained through the formation according to the invention of the casing interior extended elliptically into a fixed expansion chamber and the concentric arrangement of the piston guide ring in the cylindrical interior wall portion of the casing. Further a complicated gasket is saved on the smooth front of the piston guide ring abutting the front walls of the casing. Advantageously, it is sufficient to seal the pistons on these sides in radial direction toward the lateral portions of wall of the expansion chamber on the one hand and in their cylinders on the other hand as is customary, because the interior of the piston guide ring and the front casing walls are not required for the supply of air or fuel and for the removal of the combustion gases, as these processes can take place on the periphery of the crankcase. The interior of the piston guide ring filled with oil if need be stands under a substantially uniform pressure. A simple sealing of its side faces opposite the front walls of the casing, for instance a Seeger circlip, suffices to prevent any passage of gas from the media compressed in the cylinders into the expansion chamber or conversely all the more so because the compression process takes place only in the area of the piston guide ring during its revolution, in which it abuts tightly onto the peripheral wall of the casing. The sealing of its periphery in this area presents no difficulties as is known, since it can be produced by a rotating piston ring type of gasket. Similarly there are no difficulties in the sealing of the piston ends facing the peripheral wall of the casing.

It is clear finally that one advantage of the engine is that it can be operated with priming pump for the fuel and with a precompressor for the air if required in any particular case. In the carburetor engine version, generally no compressor is required for the supply of the gaseous air, and a compressor or priming pump i addition to the carburetor will only then be employed if a specially enhanced performance is required. The necessary air compression occurs through the compression stroke of the pistons in the piston guide ring cylinders. In

the preferred embodiment of the invention, the two interior parts of the peripheral wall of the casing are formed by overlapping bores, one of which has oval or circular cross section which joins up symmetrically to the major axis of the oval on the circular section of the other bore concentric to the piston guide ring, on which axis the center of the cylindrical bore lies, whose sectional area is preferably larger than its semicircular section. It is accordingly expedient for the diameter of the bore concentric to the piston guide ring to be approximately equal to the largest breadth of the other bore section.

The residual compression chamber, which must remain open between each of the pistons and the casing wall, can be produced according to the invention either by a chamfering of the pistonhead on the side looking away from its direction of rotation and/or a clearance of the piston guide ring made on this side, standing free in the foremost position of the piston.

BRIEF DESCRIPTION OF THE DRAWING The following are preferred embodiments of the invention as an Otto carburetor engine explained by way of example by means ofthe drawings in which:

FIG. 1 is a cross-sectional view through a rotary piston engine according to the invention with a conrod linkage of the pistons on a common piston axis;

FIG. 2 is a longitudinal section through the motor according to FIG. 1;

FIG. 3 is a variation with pistons directly articulated on the common piston axis and pivotable cylinders;

FIG. 4 is a longitudinal section through the motor according to FIG. 3; and

FIG. 5 illustrates a further embodiment.

DETAILED DESCRIPTION In the embodiment according to FIGS. 1 and 2, the crankshaft casing l is made up of a peripheral wall portion 2 and two sidewall parts 3 and 4 In the lower part of the casing interior 5 in FIG. I the casing peripheral all near 6 is formed b a cylindrical bore which is concentric to a center shaft 7 and extends upward to above the horizontal diameter 8. The top part of the casing is bounded by a peripheral wall 9 of oval section, which unites symmetrically to the vertical casing centerline If! to the ends of the cylindrical bore.

A piston guide ring I] with cylindrical periphery is supported in the cylindrical bore, its center shaft being the axis 7 and its diameter practically equal to the diameter of the cylindrical bore The piston guide ring is rotatably mounted, closefitting, in the cylindrical bore in this way. It is mounted on ball bearings 12 which are fitted each between an outer shoulder 13 of the piston guide ring and each adjacent ring portion 14 of the casing side sections 3 or 4. The peripheral casing wall 2 has shrouding rings 15 laterally, which engage in corresponding clearances of the piston guide ring which each form a shoulder and seal the ring sufficiently opposite the casing side portions 3 and 4.

The outer shoulder or each outer shoulder 13 has a firmly mounted gearwheel 16, which meshes with a driven gearwheel 17, mounted on the driven shaft (not shown in the drawing).

In the collar ring portion 14, a piston shaft 18 is mounted eccentrically to the center shaft 7, and connecting rods 19 or 20 connect pistons 21 or 22 through gudgeon pins 23 or 24 to this piston shaft. Cylinders 25 or 26 for pistons 21 or 22 run radially through the piston guide ring 11 and are aligned diametrically opposite each other.

The pistons are chamfered to a curve on the side set away from the direction of rotation 29 of piston guide ring 11 at their far ends 27 or 28. The oval bore of the casing forms an expansion chamber 30 with the piston guide ring, with an outlet passage 31 which passes through the peripheral all of the casing at the end of the chamber situated in the direction of rotation. In reach of cylindrical bore 6 concentric with the surface of the piston guide ring an inlet 32 is provided beyond the exhaust opening and in the direction of the arrow which communicates with an intake port 33 in which the fuel-air mixture flows in the direction of arrow 34 from the carburetor A prim-.

ing pump of compressor can, if desired, open additionally into the inlet 32 of the cylinder 35 of piston 36 as shown in dotted outline only by the connecting rod or crank 37 and crankshaft 38 of piston 36. If such compressor or such priming pump is provided, a back pressure valve 39 is fitted in supply line 33. Crankshaft 38 can be driven through one of the output gearwheels I7.

In the direction of the piston guide ring 11 at the beginning of expansion chamber 30, a sparkplug 40 is mounted in casing wall 2. Owing to the eccentric position of piston shaft 18 in relation to center shaft 7, the pistons 21 and 22 move with each revolution of the piston guide ring once from their furtherest radially inward position, shown for piston 22, radi ally outward as far as the position shown for piston 21 and back to the first position. The pistons are provided with gaskets 41 or 42 at their ends. Also the pistons (only partly shown) have lateral gaskets as indicated in FIG. 1 at 41a and 42a.

Each time the piston guide ring 11 rotates, the piston as soon as it passes outlet port 31 on its inward stroke produces a vacuum which causes the fuel-air mixture at inlet port 32 to be sucked into cylinder 25 or 26. In the succeeding arc of rotation of the piston guide ring extending to somewhat more than 90, the fuel-air mixture is compressed and finally at point 43 occupies only the residual compression space formed at 27 or 28 by the chamfering of the piston end to the casing wall between the extreme piston end flush with the peripheral wall of the casing and the periphery of the piston guide ring. When piston has reached position 44 shown by dotted line, spark plug 40 ignites the still heavily compressed mixture behind the piston. This now expands into expansion chamber 30, whereupon the piston comes under torque and its front end. always sitting close to expansion chamber wall 9 passes through same an in so doing its front face pushes out to and through outlet port 31 and the gas burned in the previous expansion process The preceding and succeeding operation in the expansion chamber is effected similarly by the piston opposite it at the particular time. and each time the expansion energy is transmitted to the piston guide ring and its power takeoff. the driven gear 17 for example or a shaft connected with the piston guide ring in some other way.

FIGS. 1 and 3 show also gaskets 60 which seal piston guide ring 11 against the casing wall. Theoil lubricating the cylinders in the interior of the piston guide ring is shown at 59.

The embodiment according to FIGS. 3 and 4 differs from that of FIGS. 1 and 2 only in the construction of parts 19 to 26. All other references in FIGS. 1 and 2 are equally applicable in FIGS. 3 and 4. g Y

In the embodiment according to FIGS. 3 and 4, pistons 21 a and 22a are longerin'formand are articulated to piston shaft 18 directly by their inner ends 19a or 200. Piston guide ring 11 has perforations 47. or 48 extending inward and outward, which receive the bushes 49 or 50 respectively forming the cylinders 25a or 26a respectively. These bushes are pivoted on journals 51, 52 to the piston guide ring 11, whereby their thickened ends'during the horizontal swing can slide with curved faces on correspondingly curved concave faces of the piston guide'i'ing. The respective extensions 53 and 54 at the extreme ends of th'e'respective perforations 47 and 48 form residual compression spaces, supplementary to the compression chambers formed by the respective chamferings 27 or 28 of the pistons and can also replace these latter with correspondingly larger construction On the unchamfered sides of the pistons, the. respective extensions 53 and 54 make it possible to supply gas to the cylinders ad likewise facilitate the rotation motion of the'bushings 48 and 50 here, which rotation moreover is made possibly by the extension inward of perfora tions 47 and 48.

For the rest, and the workrhg cycle during one revolution of the piston guide ring and each reciprocation of pistons 21a and 22a proceeds in 'thesa'me way as has been described for the embodiment according to FIGS. 1 and 2.

The advantage of the embodiment according to FIGS 3 and 4 as against FIGS. 1 and 2 is that it is designed for higher speeds. For that reason a more complicated construction ol the cylinders has to be taken into account.

The embodimentaccording to FIG. 5 is one variation of the embodiment according to FIGS. 3 and 4, shown in a cross section corresponding to'FIG. 3. The differences consist essentially in the followingj'.

Pistons 21b and 22b'l'iave ho chamferings on their. forward ends, but rest with their gaskets 41b and 42b respectively directly on the inside walls of casing section 2. Further, the parts forming the cylinders are not elongated bushings but cylindrical parts 49bjand 5017 respectively which are mounted to swing or turn together with pistons 21b or 22b respectively in appropriately fitting cylindrical bores in the piston guide ring.

In the support portions 49b and 50b, a roller or ball bearing swings in each in such a manner that its periphery rests on the forward-running side of piston 21b or 22b respectively. Bearing 58 serves to absorb the pressure exerted on the rear of the piston in expansion chamber 30 in the direction of rotation 29, in such a manner that the pressure received by the front of the cylinder bores of pistons 21!: and 22b and the friction on the cylinders during the piston movement is reduced.

Deviating from FIGS. 1 and 3 in the embodiment according to FIG. 5 is an inlet 32a on casing wall 2 for the working fluid, not mounted diametrically opposite the greatest radial breadth of expansion chamber30 but only a short piece of arc behind outlet passage 31 in the direction of rotation 29. The inlet passage 32a is extended by about 30 length of arc with 32b in direction 29. so that in this area the periphery of piston guide ring I] forms the inside wall of passage 32b.

On the piston end side lying back in respect to the direction of rotation. a recess is made in the bearing portion 49b and 5017 respectively and in the piston guide ring, to form the compression chamber when the appropriate piston reaches its extreme radial end position. in the case of a carburetor engine, spark plug 40 can the be fitted directly at point 57 where the piston guide ring separates from the casing wall and the expansion chamber begins.

In diesel engines, in all embodiments, the spark plug 40 is dispensed with and a diesel fuel injector nozzle connected to the usual injection or priming pump fitted in its place. Then through inlet 32 or 32a, in practice. only air for combustion from a separate compressor is introduced into the compression chamber and cylinder compression space, and compressed each time by the operating piston on its compression stroke to so high a compression, until point 57 or the injection nozzle union is reached, that when the fuel is injected the mixture ignites spontaneously with the combustion air, in the embodiments according to FIGS. 1 to 4. cylinder 35 with piston 36 can then be considered as a diagrammatic indication of a precompressor for combustion air in diesel operation and the connection 33 for the fuel-air mixture supply 34 is dispensed with.

Also in embodiment according to FIG. 1 to 4 in addition to the chamfering 27 or 28 of the pistons or in place thereof, compression chambers such as 55 and 56 can be constructed in the piston guide ring and connected with the appropriate cylinder space. This last holds good also for a carburetor engine.

The advantage of the arrangement of inlet passage 32a in direct propinquity to outlet passage 31 according to FIGS. 5 is that in the scope of the arc length of prolongation 32b of this passage, the piston starting its suction stroke over this area does not have to generate a high vacuum, but can start right away with the intake of air or air-fuel mixture. This modification according to FIG. 5 can therefore usually be recommended also for the construction according to FIGS. 1 and 4.

What i claim is:

1. A rotational piston internal-combustion engine comprising a casing defining an axis of rotation, a cylindrical piston guide ring, said cylindrical piston guide ring being rotatable and driven eccentrically inside the casing around the axis of rotation of the casing, the ring forming with said casing an expansion chamber which terminates in a gas exhaust passage. means defining an axis of rotation eccentric to said piston guide ring, no more than to pistons offset at more than to each other, said each piston being located slidably in a cylinder provided in said ring and being articulated to said means, means to keep said pistons in hermetic contact with the casing when the guide ring and the reciprocating pistons inside said ring rotate enabling fuel and air for combustion to be supplied to the cylinders in an are of the peripheral casing shell preceding the expansion chamber and to an ignition point in the direction of rotation of the guide ring, and leaving a compression space open between each piston and the casing shell for the admission of said fuel and air after each piston has made its compression stroke, the casing having a first inside wall section which is concentric to the piston guide ring and rests tightly against said piston guide ring in the area of the casing where the suction stroke and compression stroke of each of the pistons occur, and a second section which is eccentric to the axis of the guide ring at the periphery and forms with the ring said expansion chamber, each of said sections extending over an arc of about l80 for substantially the entire radial extent of said guide ring, said first wall section having an inlet for the fuel and air for combustion, said second wall sec tion being provided with said gas exhaust passage, said exhaust passage being at the end of the second section and extending over a relatively small angle compared to the angular extent of said second section, each of the said pistoris remaining in contact with said second section for almost before it reaches the region of the exhaust passage. 4

2. rotational piston engine according to claim 1 compris- 

1. A rotational piston internal-combustion engine comprising a casing defining an axis of rotation, a cylindrical piston guide ring, said cylindrical piston guide ring being rotatable and driven eccentrically inside the casing around the axis of rotation of the casing, the ring forming with said casing an expansion chamber which terminates in a gas exhaust passage, means defining an axis of rotation eccentric to said piston guide ring, no more than to pistons offset at more than 90* to each other, said each piston being located slidably in a cylinder provided in said ring and being articulated to said means, means to keep said pistons in hermetic contact with the casing when the guide ring and the reciprocating pistons inside said ring rotate enabling fuel and air for combustion to be supplied to the cylinders in an are of the peripheral casing shell preceding the expansion chamber and to an ignition point in the direction of rotation of the guide ring, and leaving a compression space open between each piston and the casing shell for the admission of said fuel and air after each piston has made its compression stroke, the casing having a first inside wall section which is concentric to the piston guide ring and rests tightly against said piston guide ring in the area of the casing where the suction stroke and compression stroke of each of the pistons occur, and a second section which is eccentric to the axis of the guide ring at the periphery and forms with the ring said expansion chamber, each of said sections extending over an arc of about 180* for substantially the entire radial extent of said guide ring, said first wall section having an inlet for the fuel and air for combustion, said second wall section being provided with said gas exhaust passage, said exhaust passage being at the end of the second section and extending over a relatively small angle compared to the angular extent of said second section, each of the said pistons remaining in contact with said second section for almost 180* before it reaches the region of the exhaust passage.
 2. A rotational piston engine according to claim 1 comprising piston guide journals pivoted in said piston guide ring and forming said cylinders, said pistons being movable in said journals.
 3. A rotational piston engine according to claim 1 wherein the piston includes a head chamfered laterally away from its direction of rotation and forming the compression space in conjunction with the first all section at the end of its compression stroke. 